Circuit Breaker Problem

I would suspect a ground fault in the phase that seems to burn out easily. (An internal short in one of the motor windings would also imbalance the phases, but it would tend to make two phases draw high.) Another possibility would be a loose cable connection at or near the breaker.

Most of my field service experience is on smaller 3 phase 220v units but I know usually by talking
to some else you usually figure it out while listening to their thoughts
On a three phase problem I check
amps on all three legs?
voltage phase to phase on all three legs?
voltage to neutral or ground on all three legs - wild leg?
are points on contactor or motor starter ok?
do you have a 3 phase protection module to monitor line conditions?
or do you have a motor starter with heated pots with 3 phase protection?
is the contactor worn with the armature not aligning correctly when pulling in?
is it possible you're losing one leg from distribution and your pump is generating
back emf to run other single phase equipment when they lose the same leg?
do you have lightning arrestors on all 3 legs?

I have found enclosed failed contactor points buy checking for voltage between
line terminal and load terminals on each leg while contactor is loaded
there should be no voltage if the points are ok

If all your equipment passes these tests I would look more strongly toward
your power supplier possibly losing a leg in their distribution and your motor
is trying to generate back emf to run other equipment burning that one leg
but getting a supplier to admit they're at fault can be difficult too
but sometimes a lineman will let the cat out of the bag

Contact your pump or motor mfg or their application engineer for a recommended 3 phase protection module if you don't have one

A module will turn off the motor when line conditions are not correct
and sometimes if conditions are too bad it may not let the motor run enough
to do any work at all but many are adjustable on voltage percentage to stop
nuisance shut downs

Good luck

i think there s an insulation fault( leading to short circuits) in the wires connected from the breaker to the motor through the starter..........since the motor s submerged , these faults can carry heavy currents and cause phase burn ......i would recommend u to check the current in each phase and also voltage between one phase n ground......

First question I have is, is it always the same phase?

If the answer to the above is "Yes", go to question 2.

2nd Question is the circuit breaker burning out on the supply or the load side?

If your answer was the load side, I would suggest that you cut the cable back at least 150mm and check the cable for dis-colouration (the cable changes colour when it has been affectived by overheating) This causes a slightly higher resistance in the cable, which is the probable cause of your problem. Higher resistance causes more heat.

But if the problem is on the supply side of the circuit breaker, my advise would be the same replace the cable or the Bus-bar suppling the CB.

Problems probally have been cause by a loose conection causing the cable to become heat damaged, you must treat the cause not the sympton.

Lets put the problem another way; If your partner gets a sexually transmitted disease (Circuit Breaker) and you gives it to you (the cable or Bus-bar), first you will want to replace your partner (circuit breaker) with a new model, and if you havent had the problem treated correctly, you will now be the carrier of the disease, and pass it on to your new partner, this will go on and on until you either chop it off or replace it.

When you have a problem like this dont just treat the sympton, treat the cause. Always cut back the cable, to ensure that the problem does not happen again.

Hope this is of help

Cheers

Joe

Thanks Joe Sparky

I got a big kick out of your answer comparing human activities
to burned cables and bus bars spreading an overheating problem

I remember hearing about the US Navy using electricity training comparing to the water pipe method
but your training method has them beat for holding student attention
and I agree totally that your suggestion to cut off the end of the bad conductor
may solve the whole problem

But I remember a job years ago where I cut back the burned conductors on a simple
30 amp phase fuse block replacement that had burned on a 220v electric furnace
as you have to remove all burnt ends of the conductors to stop the spreading
Finished job well done, turned on power, proud as punch, then stood there and watched
static electricity jump all over my new fuse block then turned to flames and reduced
my new fuse block to a pile of black powder
Sometimes you can't win them all

There must be a damage in insulation of that particular phase cable or might be the winding coil of that phase has lost enough insulation to resist the earth leakage.

In either cases, current will be higher on the particular phase than rest 2 phases and thats why due to overheating it is burning.

An easy way to trace the problem is to switch off your circuit breaker and check the resistance of your phases one by one with motor body and phase to phase.

I am sure that your faulty phase will show less resistance than others.

guys correct me if I am wrong......cheers

You approched the problem correctly:

Quickly: Check the cable to the motor for any leak between the strands (or cores). then check the motor windings if they are all the same or show differences to suggest damage to the earth or betwen them (You can connect the motor to the supply and see if it runs normally for some time and takes a balanced current on all phases..).

If all seems correct,then suspect the Circuit breaker contacts; Open and inspect: Some cheap copies of contactors and c.B. have a tendency to make weak contacts which will exhibit sparks and heatup when powered...

Hi,

Is there a joint between pump and switch board, if there is cut it off and replace otherwise there is a bad join on the particular phase that is heating.

Is your cable run not excess of manufacture specs

Check phase current -must be equal

check volt drop on phase to neutral when pump running- must be about equal

check winding insulation resistance to earth-must be equal 1M+

Use correct size of contactor rated for 100kw load

First of all, let's figure out the probable causes that make the problem happen:

1. Loose connection
2. The abnormal contact resistance
3. Under size cable
4. Unbalance voltage
5. Abnormal current flow
6. Heat generated from vicinity or inadequate cooling in the vicinity of the breaker

Out of these, loose connection is the most probable cause. There are couple of reasons for the loose connection – improper tightening, improper use of crimping tool for compression lugs, improper use of cable lugs, bad quality of circuit breaker, excess vibration, improper fixing of the circuit breaker (especially if it is plug-in type) etc.

Abnormal contact resistance may be the second most probable cause. I would suggest you to conduct the ductor test (see http://cr4.globalspec.com/thread/50934 for detail) to make sure all contacts are properly connected. If the cable is under sized, it is generating more heat at the contact point causing it burn. Unbalance voltage may also cause the phase burning with higher voltage.

The fifth and sixth ones are the least probable reasons, however you can measure the current while running the motor and make sure abnormal current is not flowing in any of the phases, and look into other heat generating elements near the breaker or inadequate cooling in the breaker area etc.

One important thing: you mentioned you are using 200A MCCB for the motor protection – is there any motor starter you are using. Motor protection should have the overload protection – do you have the overload protection for the motor?

Good luck.

- MS

http://www.ssac.com/motorpro/deftermp.htm#d

More support for my theory that back emf on an open phase 3 phase will attempt to
supply electricity to all other devices in line when a main fuse opens and burn
that phase

This site above has an excellent flash movie explaining 3 phase motor phase loss conditions it's fun to operate and cause faults on the flash movies
without major financial losses and burnt out motors

In the "Phase loss with motor running" section
Click on the "View phase loss motor running demonstration"
In their statement they state a motor can generate up to 92% of voltage in an open
phase

Imagine if you will that there is a 400A load of single phase equipment on this same leg
of a 200A motor
and you lost that phase power on at the building main or distribution mains
my theory is that a 200 amp motor will attempt to back generate this 92% voltage
into a 400 amp single phase load and burn the winding possibly before slow moving
circuit breakers, fuses or motor starters can open

A solid state motor protector of your choice or pump mfg choice of brands could help
avoid costly motor burn outs if you find this is what is happening at your location

You're getting allot of good sugestions efrnwpaluca
Good luck
John

Thank you for all your comments and i appreciate a lot. The circuit breaker is in supply side then into motor control units, wye - delta connection.